This invention relates to thermo-magnetically operated switches which utilize the saturation flux density versus the temperature characteristic of a magnetic substance to control the switching temperature, and in particular, to thermo-magnetically operated switches having two different operating points on a temperature axis.
A thermo-magnetically operated switch using magnetic materials which is constructed by positioning a permanent magnet and a magnetic substance in proximity to a reed switch whereby the contacts of the reed switch are opened and closed in response to changes in the temperature is known in the prior art as exemplified for example, by French Pat. No. 1,549,349, U.S. Pat. No. 3,295,081 and others.
Such thermo-magnetically operated switches as above mentioned are conveniently used to control the operation of devices operating in response to a predetermined temperature, because they are mechanically and thermally strong and solid, operatively stable in long use and, therefore, have a long life-time.
A typical known thermo-magnetically operated switch is of the one point operation type or of the type by which a switching operation is available at one point on a temperature axis. This restricts the fields of the use of thermo-magnetically operated switches of the known type.
We, the inventors of this invention, proposed thermo-magnetically operated switches having two different operating points, in U.S. Pat. No. 3,895,328 together with the other two joint inventors Mr. Kato and Mr. Satoh, wherein two permanent magnets and two kinds of magnetic members having different Curie points are assembled on the outer surface of a reed switch. One type of switch shown in U.S. Pat. No. 3,895,328 is one wherein it is open below a predetermined lower temperature and above a predetermined higher temperature and is closed between the lower and the higher temperatures. As this type, two arrangements are proposed, one of which is characterized by a thermo-magnetic element or a magnetic member disposed on the outer surface of a permanent magnet on the outer surface of the reed switch as shown in FIGS. 2A-8B of U. S. Pat. No. 3,895,328, the other being characterized by two permanent magnets and two kinds of magnetic members being axially arranged in cascade alongside the reed switch, as shown in FIGS. 9-11C of U.S. Pat. No. 3,895,328.
According to the former arrangement, the thermomagnetically operated switch is relatively large-sized because two kinds of parts are superposed on one another on the outer surface of the reed switch. On the other hand, the switch according to the latter arrangement is relatively small-sized because all parts are arranged in cascade alongside the reed switch without any parts superposed on the other. But since similar magnetic poles of two permanent magnets confront one another, the magnets are apt to be demagnetized. This causes undesired variations of the operating points of the switch in the course of time.
In FIGS. 12A-12C of U.S. Pat. No. 3,895,328, a thermomagnetically operated switch is also shown wherein two permanent magnets are disposed so that different poles confront one another and wherein all magnetic parts are arranged in cascade alongside the reed switch. But the switch is not the type which is open below the lower temperature and above the higher temperature and is closed between the lower and the higher temperatures (an open-close-open type), but is of the type which is closed below the lower temperature and above the higher temperature and is open between the lower and the higher temperatures (a close-open-close type).
In certain fields of use of thermo-magnetically operated switches, not the close-open-close type but the open-close-open type is required.